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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "net/quic/quic_data_writer.h"
#include <stdint.h>
#include <algorithm>
#include <limits>
using base::StringPiece;
using std::numeric_limits;
namespace net {
QuicDataWriter::QuicDataWriter(size_t size, char* buffer)
: buffer_(buffer), capacity_(size), length_(0) {
}
QuicDataWriter::~QuicDataWriter() {
}
char* QuicDataWriter::data() {
return buffer_;
}
bool QuicDataWriter::WriteUInt8(uint8 value) {
return WriteBytes(&value, sizeof(value));
}
bool QuicDataWriter::WriteUInt16(uint16 value) {
return WriteBytes(&value, sizeof(value));
}
bool QuicDataWriter::WriteUInt32(uint32 value) {
return WriteBytes(&value, sizeof(value));
}
bool QuicDataWriter::WriteUInt48(uint64 value) {
uint16 hi = static_cast<uint16>(value >> 32);
uint32 lo = static_cast<uint32>(value);
return WriteUInt32(lo) && WriteUInt16(hi);
}
bool QuicDataWriter::WriteUInt64(uint64 value) {
return WriteBytes(&value, sizeof(value));
}
bool QuicDataWriter::WriteUFloat16(uint64 value) {
uint16 result;
if (value < (UINT64_C(1) << kUFloat16MantissaEffectiveBits)) {
// Fast path: either the value is denormalized, or has exponent zero.
// Both cases are represented by the value itself.
result = static_cast<uint16>(value);
} else if (value >= kUFloat16MaxValue) {
// Value is out of range; clamp it to the maximum representable.
result = numeric_limits<uint16>::max();
} else {
// The highest bit is between position 13 and 42 (zero-based), which
// corresponds to exponent 1-30. In the output, mantissa is from 0 to 10,
// hidden bit is 11 and exponent is 11 to 15. Shift the highest bit to 11
// and count the shifts.
uint16 exponent = 0;
for (uint16 offset = 16; offset > 0; offset /= 2) {
// Right-shift the value until the highest bit is in position 11.
// For offset of 16, 8, 4, 2 and 1 (binary search over 1-30),
// shift if the bit is at or above 11 + offset.
if (value >= (UINT64_C(1) << (kUFloat16MantissaBits + offset))) {
exponent += offset;
value >>= offset;
}
}
DCHECK_GE(exponent, 1);
DCHECK_LE(exponent, kUFloat16MaxExponent);
DCHECK_GE(value, UINT64_C(1) << kUFloat16MantissaBits);
DCHECK_LT(value, UINT64_C(1) << kUFloat16MantissaEffectiveBits);
// Hidden bit (position 11) is set. We should remove it and increment the
// exponent. Equivalently, we just add it to the exponent.
// This hides the bit.
result = static_cast<uint16>(value + (exponent << kUFloat16MantissaBits));
}
return WriteBytes(&result, sizeof(result));
}
bool QuicDataWriter::WriteStringPiece16(StringPiece val) {
if (val.size() > numeric_limits<uint16>::max()) {
return false;
}
if (!WriteUInt16(static_cast<uint16>(val.size()))) {
return false;
}
return WriteBytes(val.data(), val.size());
}
char* QuicDataWriter::BeginWrite(size_t length) {
if (length_ > capacity_) {
return nullptr;
}
if (capacity_ - length_ < length) {
return nullptr;
}
#ifdef ARCH_CPU_64_BITS
DCHECK_LE(length, std::numeric_limits<uint32>::max());
#endif
return buffer_ + length_;
}
bool QuicDataWriter::WriteBytes(const void* data, size_t data_len) {
char* dest = BeginWrite(data_len);
if (!dest) {
return false;
}
memcpy(dest, data, data_len);
length_ += data_len;
return true;
}
bool QuicDataWriter::WriteRepeatedByte(uint8 byte, size_t count) {
char* dest = BeginWrite(count);
if (!dest) {
return false;
}
memset(dest, byte, count);
length_ += count;
return true;
}
void QuicDataWriter::WritePadding() {
DCHECK_LE(length_, capacity_);
if (length_ > capacity_) {
return;
}
memset(buffer_ + length_, 0x00, capacity_ - length_);
length_ = capacity_;
}
} // namespace net
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